Induction-motor.



E. THOMSON. INDUCTION MOTOR. APPLlcmpu FILED usc. n. 1913.

Patetd Apr. 6, 1915.

NON MAGNETIC lll/111111 NON MAGNETIC MAGNETIC MAGNUM;

Inventor: l'li'lf'm Thomspr His afttormeld Witnesses .v

narran sfrAfras PATENT OFFICE.l

ELIHU THOMSON, OF SWAMPSCOTT, MASSACHUSETTS, ASSIGNOR TO GENERAL :ELECTRIG COMPANY, .Ay CORPORATION 0F NEW YORK.

INDUCTION-Moron.

Specification of Letters Patent.

Patented Apr. 6, 1915.

Application tiled December 11, 1913. Serial No. 806,091.

To* all whom it may concern l Be it known that I, ELIHU THOMSON, a citizen of the United States, residingat Swampscott, county of Essex, State of Massachusetts, have invented certain new and useful Improvements in Induction-Motors, of which the following is a specification.

My inventionrelates to induction motors and particularly to those whose rotors have squirrel `cage windings.

It is well known in the art that it is desirable to have a high resistance in the secondary circuit of an induction motor when starting and a low resistance after the motor has yreached normal speed. Various means for obtaining this result Have been proposed and one well known arrangement is that wherein two windings are used, of which on'e has a low resistance and a high inductance and the other has a high resist ance but a low inductance. The inductance of a conductor is directly proportional to the frequency and since, when starting, the slip is large, the secondary currents will have a high frequency and the inductance will be proportionately large. -That winding having a high inductance will, therefore, have a high impedance and the secondary currents will flow through the other winding which has a. higher ohmic resistance, but a lower impedance. When the slip has been reduced by the speeding up of the motor, the frequency of the secondary currents will become small and the effect of self induction minimized so that the greater part of the secondary current will pass through the low resistance winding. These windings have been given various forms in order to obtain the desired result, and it is understood that one means of giving a winding a higher inductance is to sink the bars thereof below the periphery of the secondary member in order that they may be entirely surrounded by magnetic material. The consequence of such a construction is that the bars will have a higher inductancebecause of the lower reluctance of the surrounding' metal for the passage of the self induced magnetic flux.

My invention relates more particularly to the secondary windings of induction motors and the object of my invention is to provide a ,form of secondary windingJ which shall have the characteristics described above asibeing desirable and at the same time shall be simple, efiicient, and desirable from the standpoint of mechanical construction as well as of electrical efficiency." I have attained these results by making my secondary winding of -such a form that it comprises parallel circuits, one circuit having a high resistance and a low inductance, while the other has a high inductance and a low resistance. The practical embodiment of such a structure may take various forms. For instance, I may apply to the ordinary squirrel cage winding a sheath or jacket'o iron or other magnetic low reluctance, high resistance conductor. Again, I may have the bars of anford'inary squirrel oagewinding branch through parallel circuits of the requisite characteristics and interposed between the ends of the bars and the end rings. I may use the sheathed form of conductor previously mentioned for one of these circuits and bury it in the laminations andv make the other of any suitable high resistance metal, and locate it in an open groove.

I am well aware that similar results have operation thereof when applied to induc.

tion motors wllbe understood from the following description when taken in connection with the accompanying drawings in which:

Figure l is a partial longitudinal section of the Yrotor of an induction motor; Fig. 2 is a fragmental transverse section showing a single slot and a sheathed conductor embedded therein; Fig. 3 is a similar view showing a modified construction of the surrounding sheath; Fig. 4 is an elevation, partly in section, of the end of a conductor bar with its attached end ring, the end ring being sh'own as Valso sheathed; Fig. 5 is a plan view of a fragment of a rotor with branch circuits between the rotor bars and the end rings; Fig. 6 is a fragmental perspective View, partly in section, on the line 6-6 of Fig. 5; Fie'. 7 is a fragmental section on the line 7- ofl Fig. 5.

In the construction shown in Figs. l and 2, the ordinary spider 5 of the rotor carries a slotted, laminated core 6 which, is held together by means of end clamps .7 and 8 in the magnetic core of the rotor, imparts to the conductor bars a high inductance; On

" accounty of this high inductance, the impedance of the secondary winding is considerably greater when, as at starting thefrequency of the secondary currents is rela- .tively large, and` only a very small portion of these currentswill flow in the low resistlso ance of the magnetically ance member 10 of4 the magnetically clad conductor bars or in the extensions 21 or the branch 32. Instead, the greater portion of the secondary ,currents of highv frequency will be forced into the conductor of. low inductance, and will thus flow in the magnetic sheaths l1 the extensions 20. The path of the secondary currents under such circumstanceswill be of high resistance. As vthe slip of the motor decreases and the frequency of the secondary currents decreases, a greater portion of these currents will flow in the 1 clad conductor bars until the motor has attained normal slip, when substantially all the secondary currents will be carried by the low resistance bars 10 or the extensions 21. It will thus be evident that, due to the inductance of the copper bar, the effective resistclad conductor bars is relatively high for secondary currents of high frequency, and relatively low for secondary currents of low frequency.

While I haveherein shown and described low resistance member of the magnetically the preferred embodiment .of my invention,

I do not desire to limit myself to this particular arrangement. I conceive that other modi-cations embodying my invention may be developed, and I aim to include these within the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the 4United States is :---r

1. A winding induction motors including a plurality of low resistance conductors, sheaths of mag-A of bars, endl rings therefor, and a s for the secondary member of netic material thereforfsaid sheaths com l pletely incasing said conductors and providlng a current path of hi h resistance parallel to that of said conuctors, and means electrically connecting the ends of said conductors.

. 2. In the rotor of an induction motor, a

two-part squirrel cage winding, one part of said Windin being electrically insulated from the ot er part but mechanically integral therewith.

In the rotor of an induction motor, a

two-part squirrel cage winding, 'one part of said winding being electrically insulated from the other part but mechanically integral therewith, one part having a high inductance anda low resistance while the other part has aclow inductance and a high resistance. I'

4. In the rotorof lan induction motor, a squirrel cage Winding having barsy of low resistance, sheaths of magnetic material substantially incasing said bars and providing a. current path of high resistance in parallel to that of said bars.v

5. In the rotor of an induction motor, a squirrel ycage winding having bars of low stantiall incasing said bars, the bars being Iinsulate from thesheaths and both the bars and sheaths being connected by end rings.

6. A'squirrel cage winding for the rotor an induction motor comprisin copper magnetic material incasing said bars and end rings.

In witness whereof, I have hereunto'set I my hand this ninth day of December, 1913.

I ELIHU THOMSON.

`Witnesses: l

J oHN A. MCMANUS, Jr., Roem SHAND. l

"resistance sheaths of magnetic material subeath of i 

